The present invention relates generally to spring-applied, air-pressure-released parking brakes for railroad vehicle and more particularly to such parking brakes in combination with manual handbrake control devices.
In my prior U.S. Pat. 4,746,171, I described such a system including a manually operable handbrake device for selectively governing operation brakes of the brake rigging under varying conditions, for example when the air supply is disconnected from the train. This system is illustrated in FIG. 1. Although this system has been found to be valuable in certain applications, there are other applications where an inexpensive, parking brake system is needed.
Thus it is an object of the present invention to provide a parking brake system with fewer parts.
Another object is to provide a parking brake system which may be used with pre-existing equipment such as a standard freight car handbrake unit.
These and other objects of the invention are obtained by a system wherein the pivotal connection of the manual actuator or handbrake unit to the output brake lever acts as a nonfixed fulcrum of the lever which rotates in response to a given force from the brake system. When the automatically applied parking brake is manually released, it may be manually reapplied at any time. If it is simply left released; however, the automatic actuator for the parking brakes will reset the manual actuator to its reset condition and position simultaneous with release of the brakes in response to release fluid pipe pressure
The parking brake system includes an output lever having first, second and third pivot points. The output lever is pivotally connected to a brake actuating rod at the first pivot point, pivotally ConneCted to the automatic actuator at the second pivot point and pivotally connected to the manual actuator at the third pivot point. The automatic actuator pivots the output lever about the third pivot point as a fulcrum to move the first pivot point to a brake release or a brake application position in response to a release or application level of fluid pipe pressure respectively. The manual actuator pivots the output lever about the second pivot as a fulcrum to move the first pivot point to a brake release position in response to a manual activation of, for example, manual release control handles on a standard handbrake unit. The automatic actuator also moves the third pivot point from the normal release position to a manual reset position in response to the release fluid pipe pressure after manual release.
The first pivot point for the brake connection is between the second and the third pivot points for the automatic and manual actuators and equally distant therebetween. The automatic actuator includes a reset lever connected to the manual actuator for resetting the manual actuator after a manual release. The manual actuator includes a manually releaseable ratchet mechanism and a chain wound over a sheave and connected at one end to the third pivot point and at the other end to the reset lever. The automatic actuator includes a piston which is spring biased to move the first pivot point to a brake application position and is responsive to the release and application fluid pipe pressures in an air bellows acting on the piston. The air bellows may be a commercially available air spring. The manual actuator maintains the third pivot point fixed with respect to forces at the third pivot point in first direction and moveable with respect to forces at the third pivot point on second direction.
If the release pipe is the brake pipe of a standard automatic air brake system, an interlocking valve connects the automatic actuator to the brake pipe for preventing fluid flow from the automatic actuator to the brake pipe for brake pipe pressure above approximately 20 psi. A charging orifice or restriction delays or slows the fluid flow between the automatic actuator and the brake pipe.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.